The invention relates to a method of calibrating an apparatus for producing a three-dimensional object, a calibration apparatus and a method as well as an apparatus for producing a three-dimensional object.
Document EP 0 792 481 B1 discloses an apparatus for producing a three-dimensional object and a method of calibrating the control for deflecting a laser beam for rapid prototyping systems. According to this method a test pattern is generated by exposing a light-sensitive material to a laser beam at predetermined desired positions on the basis of position coordinate data. Portions of this test pattern are ditigized and the portions are combined to form an overall pattern. Correction data for the control can be calculated and provided by comparing the actual positions of the laser beam on the overall pattern with the position coordinate data. However, it is not possible to absolutely calibrate the control, because, in this method, the exact position of the light-sensitive medium in the rapid prototyping system is unknown. This is a particular disadvantage, if the rapid prototyping system is used to form an object on a presintered plate and the finished object is removed together with the plate from the rapid prototyping system, as described in document EP 0 734 842 A. The compatibility with following processes, for example the postprocessing in computer-controlled machine tools, is difficult, since the object to be formed can not be absolutely and exactly positioned on the presintered plate.
Document WO 94/15265 discloses a method of calibrating a rapid prototyping system whereby a base in the rapid prototyping system is aligned relative to a coordinate system defined by the scanner system. The base is provided with a plurality of square ink marks. The laser beam is directed to the center of each square whereby the ink is removed thereat. Thereafter the base is digitized and each center of the squares and of the radiation marks is detected to calculate correction data from the deviations therebetween.
U.S. Pat. No. 4,660,981 discloses a method and an apparatus for calibrating the deflection of a light beam using a frame arranged in the working surface of the light beam and having a plurality of holes therein. A light-sensitive detector is secured in each of the holes. Whenever the light beam is deflected onto one of the holes the corresponding detector produces a signal. In case that this signal does not correspond to the maximum signal produced if the light beam precisely hits the hole, the deflection device is re-adjusted correspondingly.
It is an object of the invention to provide an improved method of calibrating an apparatus for producing a three-dimensional object. It is a further object of the invention to provide an improved apparatus for calibrating a radiation device of an apparatus for producing a three-dimensional object. It is a still further object of the invention to provide an improved apparatus and method for producing a three-dimensional object.
According to a first aspect the invention provides a method of calibrating an apparatus for producing a three-dimensional object by solidifying a material in subsequent layers of said object at places corresponding to cross-sections of said object in said layers using a focused beam of a radiation solidifying said material, said object being built on a plate defining an invariable coordinate system which is fixed relative to said apparatus, the method comprising the steps of providing detectable reference marks on said plate for calculating said coordinate system, operating control means for deflecting said focused radiation beam to predetermined desired positions in said coordinate system, detecting the actual positions of said deflected radiation beam on said plate, determining a deviation of said actual positions from said desired positions on the basis of said reference marks, and adjusting said control means on the basis of the determined deviations.
According to a further aspect the invention provides a method of producing a three-dimensional object, comprising providing a building platform having reference marks defining an invariable machine coordinate system, forming subsequent layers of a material on said building platform, said material being solidifiable by a focused radiation beam, scanning a focused radiation beam across said layers for solidifying said material at places corresponding to cross-sections of said object in said layers, and treating said solidified object in a following processing step whereby said solidified object is aligned and/or treated using said reference marks of said building platform.
According to a still further aspect the invention provides a calibration apparatus for calibrating a radiation device of an apparatus for producing a three-dimensional object by solidifying a material in subsequent layers of said object at places corresponding to cross-sections of said object in said layers, using a focused beam of a radiation solidifying said material, said layers being formed on a plate defining a machine coordinate system which is fixed relative to said apparatus, said calibration apparatus comprising a first region having optically detectable reference marks, a second region provided with a medium which is sensitive to said radiation of said radiation device, and adjustment means for positioning said calibration apparatus at a defined position in said machine coordinate system.
According to a still further aspect the invention provides an apparatus for producing a three-dimensional object by solidifying a material in subsequent layers at places corresponding to cross-sections of said object in said layers, using a focused beam of a radiation solidifying said material, said apparatus comprising carrier means defining a machine coordinate system which is fixed relative to said apparatus, radiation means issuing said focused radiation beam, and calibration means arranged on said carrier means at defined positions in said machine coordinate system, said calibration means having a first region with optically detectable reference marks and a second region with a medium which is sensitive to said focused radiation beam.
According to a still further aspect the invention provides a method of producing a three-dimensional object, comprising providing a building platform having reference marks defining an invariable machine coordinate system, reading geometrical data defining said object in an object coordinate system, aligning said object coordinate system to said machine coordinate system, forming subsequent layers of a material on said building platform, said material being solidifiable by a focused radiation beam, and scanning a focused radiation beam across said layers for solidifying said material at places corresponding to cross-sections of said object in said layers.
According to a further development of the inventive method the test pattern is produced spatially separate from the evaluation of the test pattern. According to a further development of the method the digitized test pattern is compared with the position coordinate data and correction data for the control of the radiation device are calculated and provided on the basis of the comparison. Preferably the digitalization is made using a pixel scanner or a digital camera. According to a further embodiment the digitalization is carried out using an image recording device and a computer for subsequent digitalization.
Preferably, the reference marks used as reference features are arranged along two lines including an angle of preferably 90xc2x0 therebetween.
Preferably, a long side and a short side of a calibration plate are used as reference marks or features. Preferably, bores receiving adjustment pins are provided at the lower side of the calibration plate. Preferably adjustment pins are provided at the lower side of the calibration plate.
Preferably, the medium is a radiation-sensitive film attached to the upper side of the calibration plate. According to a further development the calibration plate is larger than the building area for the object and the first region of the calibration device having the optically detectable reference marks thereon is outside of the working area, if the calibration plate is arranged in the apparatus for producing the object.
Preferably the calibration apparatus is a calibration plate. The calibration plate has, on its upper side, a first region having optically detectable reference marks and a second region provided with a medium which is sensitive to the radiation issued by the radiation apparatus. The first region is separate from said second region.